Heater not blowing at all

[MisterB]

Just bought an '80 GMC K2500. Prior owner said the heater worked great a week ago. I tried turning it on the first time yesterday, and it doesn't blow at all on any setting.

Ideas?

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[1987 GMC Jimmy]

Check the blower fuse. Should have a dedicated, labeled 25 amp fuse on the top right of the panel. If it’s blown, there’s gonna be a wiring short somewhere most likely. Much less likely, IMO, is the blower is drawing too many amps and blew the fuse. Jump twelve volts to the blower to make sure it’s still alive (actually make sure it’s plugged in), and if it is, we can go from there.

 

[MisterB]

Check the blower fuse. Should have a dedicated, labeled 25 amp fuse on the top right of the panel. If it’s blown, there’s gonna be a wiring short somewhere most likely. Much less likely, IMO, is the blower is drawing too many amps and blew the fuse. Jump twelve volts to the blower to make sure it’s still alive (actually make sure it’s plugged in), and if it is, we can go from there.

This one? Pulled it, and it's fine. I pulled off the connectors from the blower under the hood and connected them again, but still nothing works

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[MisterB]

I also just pulled every single flat fuse in that picture, and they're all good

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[1987 GMC Jimmy]

No, I was talking about the lower slot that says aux htr/ac that doesn’t have anything in it. I thought the blower ran on a 25 amp fuse, but I don’t have any paperwork for 77-80. Did you jump power to the blower to see if it was dead?

 

[MisterB]

No, I was talking about the lower slot that says aux htr/ac that doesn’t have anything in it. I thought the blower ran on a 25 amp fuse, but I don’t have any paperwork for 77-80. Did you jump power to the blower to see if it was dead?

It's odd the previous owner said the heater worked a week ago, if indeed that spot needs a fuse. I'm not sure how to jump power like you're talking about. Can you help me with that?

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[1987 GMC Jimmy]

I don’t know if I trust this PO already. I’d go to Walmart and get an assortment of fuses to have as a backup, and you can pop a 25 in there to see what happens. You should also test the purple wire with a test lamp to see if it’s getting power. Probably best to do this with the fan selector switch set to HI. To jump it, I’d get a length of wire with some kind of pin or prong on each side and touch one side to the male prong of the blower and the other to the positive of the battery. Ground the body of the motor to the negative terminal.

 

[MisterB]

I don’t know if I trust this PO already. I’d go to Walmart and get an assortment of fuses to have as a backup, and you can pop a 25 in there to see what happens. You should also test the purple wire with a test lamp to see if it’s getting power. Probably best to do this with the fan selector switch set to HI. To jump it, I’d get a length of wire with some kind of pin or prong on each side and touch one side to the male prong of the blower and the other to the positive of the battery. Ground the body of the motor to the negative terminal.

The PO's a good person. A friend actually. It's just.. She's a girl. She bought the truck already all restored about 5 years ago, and this type of smaller stuff is likely way over her head, and so it didn't get fixed and sometimes she probably didn't even realize something needed fixing

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[1987 GMC Jimmy]

The PO's a good person. A friend actually. It's just.. She's a girl. She bought the truck already all restored about 5 years ago, and this type of smaller stuff is likely way over her head, and so it didn't get fixed and sometimes she probably didn't even realize something needed fixing

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Gotcha. Makes sense.

 

[MisterB]

I've been reading up on this some more, and it looks like I need to do a better job of finding the ground for the blower and making sure it's good. The problem is, I can't find where the damn ground is. I've heard it's on the firewall inside the engine near the blower, but where? I'm not seeing anything

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[75gmck25]

If you take a look at this picture of my A/C plenum you can see the vacuum reservoir toward the top and just to the left of it there are two ground wires connected to the firewall. The plug you can see to the right of the reservoir is for the blower motor resistors. The blower relay is also on the plenum, but hidden behind the accumulator.

Also verify whether its high speed thats not working, or the three lower speeds. The three lower speeds go through the resistors, while high speed is a direct fused power feed in the engine compartment, using the blower relay.

Bruce

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[MisterB]

If you take a look at this picture of my A/C plenum you can see the vacuum reservoir toward the top and just to the left of it there are two ground wires connected to the firewall. The plug you can see to the right of the reservoir is for the blower motor resistors. The blower relay is also on the plenum, but hidden behind the accumulator.

Also verify whether its high speed thats not working, or the three lower speeds. The three lower speeds go through the resistors, while high speed is a direct fused power feed in the engine compartment, using the blower relay.

Bruce

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I can see yours, but yours has AC and mine doesn't, so everything looks different. Also, the blower on mine doesn't blow on low, high, or anything in between

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[MisterB]

Here's what mine looks like. I got a circuit tester and tested the three wires that come out of the firewall and head over to the blower, and all light up red for positive. This is with the key turned to accessory and the heater blower switch on high. I tested the rest of the connections all the way down to the blower, and everything continues to light red. So, it's obviously getting power.

Where's the ground wire I hear people speak of?

Also, I bought some fuses, but after further inspection, that upper right fuse opening doesn't even have the metal inside with wires attached. It's just a ghost blank area.

So what now?

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[1987 GMC Jimmy]

Mine’s grounded to the firewall.

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The final step after this is to test the blower directly. It seems like you got away easy with a bad blower, but we’ll see. The aforementioned information is useful for a partial failure where the lower three or hi speed fail (rare that both the relay and resistor fail causing this condition but possible), but I get that you’re working with a total failure here. Anyway, you’re on the right track.

 

[MisterB]

Mine’s grounded to the firewall.

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The final step after this is to test the blower directly. It seems like you got away easy with a bad blower, but we’ll see. The aforementioned information is useful for a partial failure where the lower three or hi speed fail (rare that both the relay and resistor fail causing this condition but possible), but I get that you’re working with a total failure here. Anyway, you’re on the right track.

Yours looks quite a bit different than mine. I don't have that ground wire at all, as you can see, but your truck is newer than mine

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